Creation and maintenance of an ice sheet or slab for a regulation size ice skating rink having an ice surface measuring 200 feet.times.85 feet typically requires a refrigeration plant of about 300 horsepower. This refrigeration plant is usually electrically powered. Depending upon the arena construction and upon the local climate, electricity use will typically range from about 50,000 to 150,000 KWH per month during a winter skating season. Because of the escalating costs of electricity, rink closures are becoming commonplace and the development of new rinks has been greatly inhibited.
The heat load on an ice sheet, which must be removed by refrigeration, is derived from three main sources. Heat is conducted to the ice sheet from beneath and to the sides of the sheet. This heat source is usually small, seldom as much as 10% of the total heat load. Another source of the heat load to the ice sheet is convection including condensation. This heat load is transmitted to the ice sheet by circulation of air above the ice by movement of skaters, thermal differentials and the like. As the air is cooled by contact with the ice, water vapor in the air condenses and freezes, thus adding both the water heat of vaporization and fusion to the ice. The magnitude of this heat load will vary depending upon the conditions maintained within the arena but can often exceed 50% of the total heat load. A third heat source is radiation which is derived both from high temperature sources such as lights and from low temperature sources such as the arena walls and roof. This heat source is also of major proportion and can range as high as 50% or more of the total heat load.
Little can be done in the typical ice rink to reduce these heat losses while the rink is in use. However, studies of rink operations have shown that actual rink usage typically ranges from about 35% to about 50% of total available hours. For example, one arena considered to have heavy usage maintains hours of 3:00 P.M. to midnight on weekdays and from 7:00 A.M. to midnight on weekends. In this example, the ice is in use for 79 of the 168 available hours, or 47% of the time.
It would seem obvious to emplace an insulating cover over the ice sheet during non-operating hours in order to substantially eliminate convection and condensation heat load and to drastically reduce the radiation heat load. Such approaches have always been dismissed as being utterly impracticable to implement on a daily operating basis because of the time, labor and equipment required to place and remove a covering over the nearly 1/2 acre expanse of the regulation size rink. Compounding the problem is the fact that a typical rink maintains only a skeleton crew on duty during those non-use hours when installation and removal of a covering would be feasible.
It is common to cover athletic fields such as football fields and the like to keep them dry in preparation for a game. However, in those instances large crews are available, insulating value of the tarpaulin or like covering is of little consequence or concern and the installation-removal procedure is done infrequently rather than on a daily basis. Nevertheless, a number of specialized devices have been developed to cover athletic fields. Examples include U.S. Pat. No. 3,108,804 which describes a pair of laterally spaced mobile units having a tubular reel member supported between them. A tarpaulin is rolled upon the reel is stored position and the tarpaulin is unrolled over the surface of a playing field as the mobile units are advanced. U.S. Pat. No. 3,395,918 describes a tarpaulin cover for an athletic field which is wound upon a reel which is mounted on an end-pivoted carrier. It is also known to lay down large expanses of plastic film on ground surfaces as an agricultural mulch and like purposes. One example of a device for covering large fields with a unitary film is described in U.S. Pat. No. 4,050,972.